Method and apparatus for adjusting mobility parameter

ABSTRACT

A mobility parameter adjustment method and apparatus for use in a wireless communication system is provided. The mobility parameter adjustment method of a base station includes receiving connection failure information from a terminal, and adjusting a mobility adjustment parameter based on the connection failure information. The mobility parameter adjustment method and apparatus of the present disclosure is capable of adjusting mobility parameter efficiently so as to improve the mobility robustness of the wireless communication system and User Equipment (UE).

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.14/820,146, filed on Aug. 6, 2015 which is a continuation of U.S. patentapplication Ser. No. 13/956,850, filed on Aug. 1, 2013, which has issuedas U.S. Pat. No. 9,131,411 on Sep. 8, 2015 and claimed the benefit under35 U.S.C. §119(a) of a Korean patent application filed on Aug. 3, 2012in the Korean Intellectual Property Office and assigned Serial No.10-2012-0085245, and of a Korean patent application filed on Jan. 30,2013 in the Korean Intellectual Property Office and assigned Serial No.10-2013-0010258, the entire disclosure of each of which is herebyincorporated by reference.

TECHNICAL FIELD

The present disclosure relates to a method and apparatus for adjusting amobility parameter in a wireless communication system.

BACKGROUND

Mobile communication systems have been developed to provide a user theability to communicate while on the move. With the rapid advance oftechnologies, mobile communication systems have evolved such that theyare now capable of providing a high speed data communication service aswell as a voice telephony service.

FIG. 1 is a diagram illustrating a wireless communication systemaccording to the related art.

Referring to FIG. 1, the wireless communication system includes a radioaccess network 130 and a core network 140. The radio access network 130includes a base station 120. A terminal 100 and the base station 120 areconnected through a radio link 110, and other nodes of the wirelesscommunication system are connected through wired links. The base station120 includes one or more cells, each cell has a certain service coveragearea, and the terminal 100 is served within the cell coverage. Here, thecell means the cell of the cellular communication system and althoughthe base station 120 is a device for managing and controlling the cell,the terms “base station” and “cell” are used interchangeably forconvenience.

If the terminal 100 moves out of the range of the serving cell or if itis predicted that the terminal 100 will move out of the range of theserving cell, a new cell prepares to serve the terminal 100 toseamlessly provide the terminal with service. This process of changingthe serving cell is referred to as handover. The cell serving theterminal 100 before the handover is called the source cell, and the cellto serve the terminal 100 after the handover is called the target cell.

The terminal 100 measures signals from the cells and reports themeasurement results to the serving cell. The terminal 100 may measuresignals of the serving cell and one or more neighbor cells. The cellreceiving the measurement report makes a handover decision based on atleast one of the reported measurement information and a previouslystored mobility parameter. If the mobility parameter is set to anappropriate value, the handover is triggered at an appropriate time.

FIGS. 2A, 2B, and 2C are diagrams illustrating situations of connectionfailure due to the mobility parameter set inappropriately according tothe related art. The connection failure may occur when the handover isnot triggered at a supposed time (Radio Link Failure, RLF) or in themiddle of the handover process (HandOver Failure, RLF).

FIG. 2A is a message flow diagram illustrating a situation of Too LateHandover (TLH) according to the related art.

In FIG. 2A, the mobility parameter of the cell 200 is configured so asto have a tendency of triggering handover too late. In this case, thecell 200 may continue serving the terminal 215 which is no longer in theservice range of the cell 200 so as to cause connection failure asdenoted by reference number 210. The terminal 215 may establish aconnection to another cell 205 after the connection failure 210. Sincethe TLH has occurred due to the misconfigured mobility parameter of thecell 200, it is necessary to adjust the mobility parameter of the cell200. In FIG. 2A, the situation is expressed in such a way that TLH hasoccurred to the cell 205.

FIG. 2B is a message flow diagram illustrating a situation of Too EarlyHandover (TEH) according to the related art.

In FIG. 2B, the mobility parameter of the cell 220 is configured so asto have a tendency of triggering handover too early. In this case, thecell 220 may forcibly trigger a handover of the terminal 240 which isstill in the service range of the cell 220. This may cause connectionfailure after successful handover as denoted by reference number 230 orconnection failure in the middle of handover process as denoted byreference number 235. The terminal 240 re-establishes a connection withthe cell 220 after experiencing one of the connection failures after thesuccessful handover and in the middle of the handover process. Since theTEH has occurred due to the misconfigured mobility parameter of the cell220, it is necessary to adjust the mobility parameter. In FIG. 2B, thesituation is expressed in such a way that TEH has occurred to the cell225.

FIG. 2C is a message flow diagram illustrating a situation of Handoverto Wrong Cell (HWC) according to the related art.

Referring to FIG. 2C, if the mobility parameter of the cell 250 isconfigured so as to have a tendency of triggering handover to a cell 255configured with an incorrect mobility parameter, the cell 250 maytrigger the handover to the cell 255, which is the wrong cell, ratherthan the cell 270, whose service coverage area the terminal 275 hasactually entered, so as to cause connection failure after successfulhandover as denoted by reference number 260 or connection failure in themiddle of handover process as denoted by reference number 265. Theterminal 275 establishes a connection to the cell 270 after experiencingone of the connection failures after successful handover and in themiddle of handover process. Since HWC has occurred due to themisconfigured mobility parameter of the cell 250, it is necessary toadjust the mobility parameter. In FIG. 2C, the situation is expressed insuch a way that HWC has occurred to the cell 255 or HWC has occurredinstead of handover to the cell 270.

It is possible to reduce the frequency of the occurrence of TLH, TEH,and HWC by transmitting, by the cell which has failed the attemptedconnection, the connection failure information to a new target cell,delivering the connection failure information to the cell whose mobilityparameter is necessary to be adjusted, and adjusting the mobilityparameter of the corresponding cell. This means the improvement ofmobility robustness. Long Term Evolution (LTE) defines a connectionfailure detection mechanism of the cell of which mobility parameteradjustment is required only when the User Equipment (UE) which hasfailed connection attempts Radio Resource Control (RRC) re-establishmentto a new cell.

However, the current handover mechanism has drawbacks in that 1) theconnection failure information stored in the UE may be transmitted, withpartial omission, to the cell requiring mobility parameter adjustment,2) the terminal cannot detect any connection failure without attempt ofRRC re-establishment, and 3) a method of adjusting the mobilityparameter after detecting the connection failure is not specified.Therefore, there is a need for an apparatus and a method capable ofimproving the mobility robustness to overcome the above problem.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present disclosure.

SUMMARY

Aspects of the present disclosure are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly an aspect of the presentdisclosure is to provide a method and apparatus for adjusting a mobilityparameter efficiently.

In accordance with an aspect of the present disclosure, a mobilityparameter adjustment method of a base station is provided. The methodincludes receiving connection failure information from a terminal, andadjusting a mobility adjustment parameter based on the connectionfailure information.

In accordance with another aspect of the present disclosure, a basestation for adjusting a mobility parameter is provided. The base stationincludes a communication unit configured to receive connection failureinformation from a terminal, and a control unit configured to adjust themobility parameter based on the connection failure information.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present disclosure will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a diagram illustrating a wireless communication systemaccording to the related art;

FIG. 2A is a message flow diagram illustrating a situation of Too LateHandover (TLH) according to the related art;

FIG. 2B is a message flow diagram illustrating a situation of Too EarlyHandover (TEH) according to the related art;

FIG. 2C is a message flow diagram illustrating a situation of Handoverto Wrong Cell (HWC) according to the related art;

FIG. 3 is a flowchart illustrating a mobility parameter adjustmentmethod of an evolved Node B (eNB) according to an embodiment of thepresent disclosure;

FIG. 4 is a signal flow diagram illustrating signal flows for connectionfailure information transmission in a mobility parameter adjustmentmethod according to an embodiment of the present disclosure;

FIG. 5 is a flowchart illustrating a connection failure detectionprocedure of a mobility parameter adjustment method according to asecond embodiment of the present disclosure;

FIG. 6 is a block diagram illustrating a configuration of an eNBaccording to an embodiment of the present disclosure; and

FIG. 7 is a block diagram illustrating a configuration of a UserEquipment (UE) according to an embodiment of the present disclosure.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the present disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of the presentdisclosure. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of the presentdisclosure. Accordingly, it should be apparent to those skilled in theart that the following description of various embodiments of the presentdisclosure is provided for illustration purpose only and not for thepurpose of limiting the present disclosure as defined by the appendedclaims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

Although the description is directed to a Long Term Evolution (LTE)radio access network and core network and Evolved Packet Core (EPC)specified in the 3^(rd) Generation Partnership Project (3GPP), it willbe understood by those skilled in the art that the present disclosurecan be applied to other communication systems having a similar technicalbackground and channel format, with a slight modification, withoutdeparting from the spirit and scope of the present disclosure.

FIG. 3 is a flowchart illustrating a mobility parameter adjustmentmethod of an evolved Node B (eNB) according to an embodiment of thepresent disclosure.

Referring to FIG. 3, the eNB receives connection failure information atoperation 390. A method of receiving connection failure information isdescribed with reference to FIG. 4.

FIG. 4 is a signal flow diagram illustrating signal flows for connectionfailure information transmission in a mobility parameter adjustmentmethod according to an embodiment of the present disclosure.

According to an embodiment of the present disclosure, the terminal 300may undergo connection failure and transmit the connection failureinformation. The eNBs 310 and 320 may exchange the connection failureinformation through an inter-eNB interface. According to an embodimentof the present disclosure, the connection failure information may betransmitted to the cell of which mobility parameter is required.

Referring to FIG. 4, the UE 300 undergoes connection failure atoperation 325. The terminal 300 which has experienced the connectionfailure sends a message including the connection failure information toa new eNB 310 at operation 330. This message may be any ofRRCConnectionReestablishmentComplete message, RRCConnectionReestablishmentRequest message, and UEInformationResponsemessage. The connection failure information may include the informationcollected from at least one of the cell serving the terminal before theoccurrence of the connection failure and the neighbor cells. Theinformation collected from at least one cell may include the barring ornon-barring state per cell, minimum required RX level from the cell,minimum required quality level from the cell, maximum Transmission (Tx)power level, and the like.

If the eNB 310 to which the UE 300 has established a connection afterconnection failure is not the base station managing the cell for whichmobility parameter adjustment is required, the UE 300 which has receivedthe connection failure information from the UE 300 sends the eNB 320managing the cell for which mobility parameter adjustment is required amessage including the connection failure information in operation 340.This message is delivered from the eNB 310 to the eNB 320 directly orrelayed by another eNB. The message may be one of HANDOVER REPORTmessage and RLF INDICATION message. The connection failure informationmay include at least one of the information collected by the terminaland RLF report.

If the connection failure information is received from the UE 300, theeNB 310 determines whether the eNB to which the correspondinginformation is addressed or of which mobility parameter is required tobe adjusted according to the connection failure information is the eNB310 itself If it is determined that the eNB of which the mobilityparameter is required to be adjusted is the eNB 310 itself, the eNB 310adjusts its mobility parameter based on the connection failureinformation. If it is determined that the eNB of which the mobilityparameter is required to be adjusted is not the eNB 310 itself, the eNB310 transmits the connection failure information to the eNB whosemobility parameter is required to be adjusted.

Returning to FIG. 3, if the connection failure information is received,the eNB determines the reason for the connection failure based on theconnection failure information at operation 392. A mode of operation 392is described with reference to FIG. 5.

FIG. 5 is a flowchart illustrating a connection failure detectionprocedure of a mobility parameter adjustment method according to asecond embodiment of the present disclosure.

According to the second embodiment, the radio access network may detectthe connection failure regardless of RRC reestablishment. Using thisfeature, a method for detecting the connection failure regardless of RRCreestablishment is disclosed. The eNB of the radio access networkaccording to the second embodiment may use the connection failureinformation received from at least one of the terminal or another eNBaccording to the first embodiment to detect the connection failure.

Referring to FIG. 5, when connection failure occurs, it is possible todetect one of TLH 480, TEH 483, and HWC 485.

In FIG. 5, connection failure occurs at operation 400. The cell A isconfigured as the cell in which the UE has most recently stayed beforethe connection failure at operation 410.

The eNB determines whether the RRC reestablishment has been attemptedfor the duration until the UE connects to the eNB normally since theconnection failure at operation 420. If the RRC reestablishment has beenattempted for the duration, the procedure goes to operation 425 and,otherwise, to operation 430. If the RRC reestablishment has beenattempted for the corresponding duration, the cell B is configured asthe cell to which the UE has attempted the RRC reestablishment firstsince the connection failure at operation 425. If the RRCreestablishment has not been attempted for the corresponding duration,the cell B is configured as the best cell analogized from the connectionfailure information, i.e. best cell that might serve the UE mostappropriately at the time of connection failure, at operation 430.

The eNB determines whether any handover of the corresponding UE has beentriggered for a certain duration before the occurrence of the connectionfailure at operation 440. If no handover of the corresponding UE hasbeen triggered for the certain duration before the occurrence of theconnection failure, the procedure goes to operation 470. If any handoverof the corresponding UE has been triggered for a predetermined durationbefore the occurrence of the connection failure, the procedure goes tooperation 445.

The eNB determines whether the cell A is identical with the cell B atoperation 470. If the cell A is identical with the cell B, this means anerror has occurred at operation 465. In this case, the eNB may performan appropriate error handling process or ends the procedure withoutextra handling. If the cell A is not identical with the cell B, the celldetermines the situation as Too Late Handover (TLH) at operation 480. Atthis time, it may be determined that the handover from cell A to cell Bhas occurred too late. Accordingly, there is a need of adjusting themobility parameter such that the handover from the cell A to the cell Boccurs at an earlier time.

In some embodiments, the operation of determining whether the two cellsmatch may be the operation of determining whether the identifiers of thetwo cells match each other. According to another embodiment of thepresent disclosure, the operation of determining whether the two cellsmatch each other may be the operation of determining whether the RadioAccess Technology (RAT) of one cell is identical with the RAT of anothercell.

According to a modified embodiment, if the handover of the UE is nottriggered in a certain time since the connection failure, this situationmay be regarded as TLH without determination of whether the cells A andB match. Although it is not a precise method and thus may misjudge theconnection failure reason as TLH, this method is advantageous inprocessing simplicity.

In summary, if any connection failure has occurred, if RRCreestablishment has been attempted, if no handover has been triggered ina certain time (certain time duration) before the connection failure,and if the cell (cell A) in which the terminal most recently receivedservice before the connection failure differs from the cell (cell B) towhich the terminal has attempted RRC reestablishment first, it isdetermined that the reason of connection failure is TLH.

If any connection failure has occurred, if no RRC reestablishment hasbeen attempted before the UE connects to the eNB normally since theconnection failure, if no handover has been triggered in a predeterminedduration before the connection failure, if the cell (cell A) in whichthe UE most recently received service before the connection failure andthe cell (cell B) which is analogized, based on the connection failureinformation, as the best cell at the time when the connection failurehas occurred differ from each other, it is determined that TLH is thereason of handover failure.

In the case that the handover has been triggered in a certain timebefore the connection failure at operation 440, the cell C is configuredas the source cell of the handover triggered most recently before theconnection failure at operation 445. Likewise, the cell D is configuredas the target cell of the handover triggered most recently at operation447. The eNB determines whether the cells B and C are identical witheach other at operation 455. If the cells B and C are identical witheach other, the eNB assumes that the reason of the connection failure isTEH at operation 483. At this time, it is determined that the handoverfrom the cell C to the cell D has occurred too early. Accordingly, it isnecessary to adjust the handover from the cell C to the cell D to occurat a time later.

Operation 483 can be summarized as follows: if connection failure hasoccurred, if the UE has attempted RRC reestablishment until the UEconnects to the eNB since the connection failure, if no handover hasbeen triggered in a certain time before the occurrence of the connectionfailure, if the cell (cell B) to which the RRC reestablishment has beenattempted is identical with the source cell (cell C) of the handoverwhich has been triggered lastly before the occurrence of the connectionfailure, it is determined that the reason of the connection failure isTEH.

Also, if connection failure has occurred, if no RRC reestablishment hasbeen attempted until the UE connects to the eNB normally since theconnection failure, if no handover has occurred in a certain durationbefore the connection failure, if the cell (cell B) which is analogizedas the best cell for serving the UE at the time when the connectionfailure has occurred is identical with the source cell (cell C) of thehandover triggered lastly before the connection failure, the eNBdetermines that the reason of the connection failure is TEH at operation483.

If it is determined that the cells B and C are not identical with eachother at operation 455, the eNB determines whether the cells B and D areidentical with each other at operation 460. If the cells B and D are notidentical with each other, it may be analogized that the reason of theconnection failure is HWC at operation 485. At this time, it isdetermined that the handover has been performed to the cell D wrongly inthe situation that the handover should have been performed from the cellC to cell B. Accordingly, it is necessary to adjust the mobilityparameter such that the handover from the cell C to the cell B occurs ata time later or earlier. The two kinds of adjustments may be performedsimultaneously.

That is, if the connection failure has occurred, if the RRCreestablishment has been attempted until the UE has connected to the eNBnormally since the connection failure, if handover has been triggered ina certain duration before the occurrence of the connection failure, andif the cell (cell B) attempted RRC reestablishment first since theconnection failure differs from the source cell (cell C) of the handovertriggered lastly before the occurrence of the connection failure and thetarget cell (cell D), the eNB determines that the reason of theconnection failure is HWC at operation 485.

Also, if the connection failure has occurred, if no RRC reestablishmenthas been attempted until the UE has connected to the eNB normally sincethe connection failure, if a handover has been triggered in a certaintime duration before the connection failure, and if the cell (cell B)analogized as the best cell for serving the UE at the time of theconnection failure based on the connection failure information differsfrom the source cell (cell C) of the handover triggered lastly beforethe connection failure and the target cell (cell D), the eNB determinesthat the reason of the connection failure is HWC at operation 485.

If it is determined that the cells B and D are identical with each otherat operation 460, this is judged as an erroneous situation at operation465 and thus the eNB performs an error handling process or ends theprocedure without taking any action.

In the above described connection failure detection methods, the cellanalogized as the best cell for serving the UE at the time of theconnection failure based on the connection failure information atoperation 430 may be one of the cells from which the measurementinformation contained in the RLF report have been collected. The eNBanalogizes the cell based on at least one Evolved universal terrestrialradio access network Cell Global Identifier (ECGI) including a PublicLand Mobile Network (PLMN) identifier, a Closed Subscriber Group (CSG)identifier, Reference Signal Received Power (RSRP), Reference SignalReceived Quality (RSRQ), a barring policy, a minimum required RX level,a minimum required quality level, and a maximum TX power level, of thecell from which the measurement information is collected. The analogizedcell (cell B at operation 430) may be one of the best-measured cellbefore the connection failure, a suitable cell likely to be selected inapplying the cell selection rule, and the cell having established an RRCconnection first since the connection failure.

Returning to FIG. 3, the eNB adjusts the mobility parameter according toat least one of the connection failure information and analogizedconnection failure reason at operation 394.

The eNB managing the cell requiring mobility parameter adjustmentadjusts the mobility parameter. The eNB may use at least one of theconnection failure information received from at least one of the UE andother eNBs and the connection failure reason analogized through theprocedure of FIG. 5 for adjustment of the mobility parameter. The eNB iscapable of adjusting the mobility parameter appropriately based on thecollected information.

Assuming that the mobility parameter of the cell before mobilityparameter adjustment is P _(old) and the adjusted mobility parameter isP _(new), P _(old) and P _(new) can be considered as vectors in the samedimension (in case of 1 dimension, scalar). According to a thirdembodiment, P _(new) can be acquired using Equation (1):

P _(new) = P _(old) + H   (1)

In Equation (1), H denotes a function, codomain elements of H arevectors or scalars having the same dimension, and the element of thedomain of H may have a form of one of a set and a vector. The elementsof the domain may include at least one of P _(old) and entire (partial)information collected by the eNB managing the cell requiring mobilityparameter adjustment. The information collected by the eNB may includeat least one of connection failure information received from at leastone of the terminal and other eNBs through the procedure of FIG. 4 andthe connection failure reason acquired through the procedure of FIG. 5.

Although P _(new) is acquired by adding H to P _(old) in the abovedescribed method, it is obvious to those in the art that the P _(new)can be acquired through another method by modifying H appropriately inthe above described method.

H can be configured to satisfy at least one of the following conditions.

-   -   i. If it is determined, based on the collected information, that        TLH has occurred to a specific cell frequently, P _(new) is        adjusted to trigger the handover to the specific cell earlier as        compared to P _(old).    -   ii. If it is determined, based on the collected information,        that TEH has occurred to a specific cell frequently, P _(new) is        adjusted to trigger the handover to the specific cell later as        compared to P _(old).    -   iii. If it is determined, based on the collected information,        that HWC has occurred to a specific cell frequently, P _(new) is        adjusted to trigger the handover to the specific cell later as        compared to P _(old).    -   iv. If it is determined that HWC has occurred frequently instead        of handover to a specific cell, P _(new) is adjusted to trigger        the handover to the specific cell earlier as compared to P        _(old).    -   v. The magnitude of an element of H is determined based on at        least one of P _(old) and measurement information included in        the connection failure information.    -   vi. If it is determined, based on the collected information,        that TLH has occurred to a specific cell frequently, P _(new) is        adjusted to trigger the handover to the specific cell earlier as        compared to P _(old).    -   vii. if it is determined, based on the collected information,        that TEH has occurred to a specific cell frequently, P _(new) is        adjusted to trigger the handover to the specific cell later as        compared to P _(old).

In the above method, the criteria for judging frequent occurrence ofTLH, TEH, or HWC and adjustment of the mobility parameter to trigger thehandover earlier or later can be configured per eNB.

FIG. 6 is a block diagram illustrating a configuration of an eNBaccording to an embodiment of the present disclosure.

As shown in FIG. 6, the eNB 600 includes a communication unit 610 and acontrol unit 620. The communication unit 610 is responsible forcommunication of the terminal 600 with network entities. The controlunit 620 controls overall operations of the eNB. The eNB 600 may includefurther components in addition to the communication unit 610 and thecontrol unit 620. However, illustrations of the components that are notrelated to the present disclosure are not depicted in the drawing.

In an embodiment of the present disclosure, the communication unit 610sends the connection failure information received from the UE to thecontrol unit 620 or another eNB. The communication unit 610 is alsocapable of transmitting handover command and other control messages tothe UE under the control of the control unit 620.

According to an embodiment of the present disclosure, the control unit620 is capable of analogizing the connection failure region from theconnection failure information transmitted by the UE. The control unit620 is also capable of adjusting a mobility parameter according to theanalogized connection failure reason and/or connection failureinformation. The method for adjusting the mobility parameter has beendescribed with reference to operation 394 of FIG. 3. The control unit620 makes a handover decision based on the adjusted mobility parameterand controls the communication unit 610 to transmit a handover command.

FIG. 7 is a block diagram illustrating a configuration of a UE accordingto an embodiment of the present disclosure.

As shown in FIG. 7, the terminal 700 includes a communication unit 710and a control unit 720. The communication unit 710 is responsible forcommunication of the terminal 700 with a base station and other networkentities. The control unit 720 controls overall operations of theterminal 700. The terminal 700 may further include other components inaddition to the communication unit 710 and the control unit 720.However, illustrations of the components that are not related to thepresent disclosure are not depicted in the drawing.

The communication unit 710 may receive a handover command from the eNB.The control unit 710 is capable of controlling the communication unit720 to perform handover according to the handover command. Whenconnection failure occurs, the control unit 720 generates connectionfailure information and controls the communication unit 710 to transmitthe connection failure information to the eNB connected afterward.

As described above, a mobility parameter adjustment method and apparatusof the present disclosure is capable of adjusting a mobility parameterefficiently so as to improve the mobility robustness of the wirelesscommunication system and UE.

It will be understood that each block of the flowchart illustrationsand/or block diagrams, and combinations of blocks in the flowchartillustrations and/or block diagrams, can be implemented by computerprogram instructions. These computer program instructions may beprovided to a processor of a general purpose computer, special purposecomputer, or other programmable data processing apparatus to produce amachine, such that the instructions, which execute via the processor ofthe computer or other programmable data processing apparatus, createmeans for implementing the functions/acts specified in the flowchartand/or block diagram block or blocks. These computer programinstructions may also be stored in a computer-readable memory that candirect a computer or other programmable data processing apparatus tofunction in a particular manner, such that the instructions stored inthe computer-readable memory produce an article of manufacture includinginstruction means which implement the function/act specified in theflowchart and/or block diagram block or blocks. The computer programinstructions may also be loaded onto a computer or other programmabledata processing apparatus to cause a series of operational steps to beperformed on the computer or other programmable apparatus to produce acomputer implemented process such that the instructions which execute onthe computer or other programmable apparatus provide steps forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

Furthermore, the respective block diagrams may illustrate parts ofmodules, segments or codes including at least one or more executableinstructions for performing specific logic function(s). Moreover, itshould be noted that the functions of the blocks may be performed indifferent order in several modifications. For example, two successiveblocks may be performed substantially at the same time, or may beperformed in reverse order according to their functions.

The term “module” according to embodiments of the disclosure, means, butis not limited to, a software or hardware component, such as a FieldProgrammable Gate Array (FPGA) or Application Specific IntegratedCircuit (ASIC), which performs certain tasks. A module mayadvantageously be configured to reside on the addressable storage mediumand configured to be executed on one or more processors. Thus, a modulemay include, by way of example, components, such as software components,object-oriented software components, class components and taskcomponents, processes, functions, attributes, procedures, subroutines,segments of program code, drivers, firmware, microcode, circuitry, data,databases, data structures, tables, arrays, and variables. Thefunctionality provided for in the components and modules may be combinedinto fewer components and modules or further separated into additionalcomponents and modules. In addition, the components and modules may beimplemented such that they execute one or more CPUs in a device or asecure multimedia card.

The foregoing disclosure has been set forth merely to illustrate thedisclosure and is not intended to be limiting. Since modifications ofthe disclosed embodiments incorporating the spirit and substance of thedisclosure may occur to persons skilled in the art, the disclosureshould be construed to include everything within the scope of theappended claims and equivalents thereof

While the present disclosure has been shown and described with referenceto various embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present disclosure asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method by a first base station, the methodcomprising: triggering a handover for a terminal; and receiving a firstmessage including radio link failure information from a second basestation based on a reason for a radio link failure of the terminal,wherein the reason for the radio link failure of the terminal isidentified based on the radio link failure information.
 2. The method ofclaim 1, wherein a second message including the radio link failureinformation is received by the second base station from a third basestation which received information related to a failure from theterminal, and wherein the radio link failure information included in thesecond message is transferred to the first base station by using thefirst message.
 3. The method of claim 1, wherein the first messageincludes a handover report message.
 4. The method of claim 2, whereinthe second message includes a radio link failure indication message. 5.The method of claim 1, wherein the first base station is a network nodeof which the mobility parameter is required to be adjusted based on thereason for the radio link failure.
 6. The method of claim 1, wherein theradio link failure information is used to identify a cell for servingthe terminal at the time of the radio link failure.
 7. The method ofclaim 1, further comprising: adjusting a mobility parameter based on theradio link failure information.
 8. A first base station comprising: acommunication unit configured to transmit and receive a signal; and acontrol unit configured to: trigger a handover for a terminal, andreceive a first message including radio link failure information from asecond base station based on a reason for a radio link failure of theterminal, wherein the reason for a radio link failure of the terminal isidentified based on the radio link failure information.
 9. The firstbase station of claim 8, wherein a second message including the radiolink failure information is received by the second base station from athird base station which received information related to a failure fromthe terminal, and wherein the radio link failure information included inthe second message is transferred to the first base station by using thefirst message.
 10. The first base station of claim 8, wherein the firstmessage includes a handover report message.
 11. The first base stationof claim 9, wherein the second message includes a radio link failureindication message.
 12. The first base station of claim 8, wherein thefirst base station is a network node of which the mobility parameter isrequired to be adjusted based on the reason for the radio link failure.13. The first base station of claim 8, wherein the radio link failureinformation is used to identify a cell for serving the terminal at thetime of the radio link failure.
 14. The first base station of claim 8,wherein the control unit is further configured to adjust a mobilityparameter based on the radio link failure information.